1. Field of the Invention
The present invention generally relates to an apparatus for measuring differential pressure between different regions, sites or positions of a tube through which a substance such as a light can flow.
Priority is claimed on Japanese Patent Application No. 2006-67470, filed Mar. 13, 2006, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Some examples of the conventional differential pressure measuring apparatus have been known. The conventional differential pressure measuring apparatus is configured to measure a differential pressure between the opposite sides of an orifice plate that is disposed in a tube through which a liquid can flow. A first example of the conventional differential pressure measuring apparatuses uses connecting tubes that are connected with the tube on the opposite sides of an orifice plate. The connecting tubes are configured to draw the liquid from the opposite sides of the orifice plate into the connecting tubes so that the pressures of the liquid on the opposite sides of the orifice plate travel through the connecting tubes.
Further, the connecting tubes are connected to each other through a three-valve. The pressures of the liquid on the opposite sides of the orifice plate travel through the connecting tubes and reach the three-valve at which detectors are provided. The traveled liquid pressures are then detected by the detectors. The detected pressures are then compared to each other to measure a differential pressure of the liquid between the opposite sides of the orifice plate, based on the detected pressures.
A second example of the conventional differential pressure measuring apparatus uses capillary tubes that are connected with a tube on the opposite sides of an orifice plate that is disposed in the tube through which a liquid can flow. The capillary tubes are filled with a sealed liquid such as silicone oil. The capillary tubes are not designed to allow a continuing flow of liquid. The liquid that is sealed in the capillary tube may act as a pressure-traveling medium that causes the liquid pressure to travel through it. The traveled pressures of the sealed liquid are then detected to measure a differential pressure between the opposite sides of the orifice plate, based on the detected pressures.
As described above, the first example of the conventional differential pressure measuring apparatus is configured to draw a liquid from the tube into the connecting tubes. The connecting tubes are narrower than the tube. If the liquid contains a solid material or has a high viscosity, then the liquid may flow through the tube while causing a clog of a liquid flow in the connecting tube. In other cases, the connecting tubes may be corroded or broken to cause a leakage of the liquid from them.
As described above, the second example of the conventional differential pressure measuring apparatus uses the capillary tubes that are filled with a sealed liquid. The capillary tube is a very narrow tube. The liquid that is sealed in the capillary tube may have an increased viscosity at a decreased ambient temperature. The increased viscosity provides an increased viscous resistance that inhibits the liquid pressure to travel through the capillary tube. This may deteriorate the sensitivity of the differential pressure measuring apparatus.
In other cases, the capillary tube may have a temperature difference over positions thereof In other words, a local area of the capillary tube may be different in temperature from the remaining portion thereof This temperature difference may cause the sealed liquid to exhibit a local thermal expansion at the different-temperature portion of the capillary. The local thermal expansion causes a local volumetric change of the sealed liquid. The local volumetric change may disturb the pressure of the sealed liquid from traveling through the capillary tube. As a result, the traveled pressure is different from the original pressure. The temperature difference or variation over the capillary tube may deteriorate the sensitivity of the differential pressure measuring apparatus.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved apparatus and/or method. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.